Wierd Dating ?

[72 Cheyenne K20]

I just got my 71 Blazer and noticed the blue door date sticker was painted over. I wanted to see if was the oricinal door so I scraped the paint off. Sure as crap, same vin as the title and glove box. But, the date in the upper right corner says 8/70. I feel pretty sure the original engine is still in it. I ran the numbers on the right side of the block just in front of the valve cover and looks like the block date (V0729TBG) is July,29 1971 and for a k10 - 2500. Anyone have a clue?

Thanks, Scott